1. Field Of The Invention
While this invention relates to the abradable seal art generally, it is particularly adapted for use in sealing fluids of aircraft gas turbines and the like.
2. Description Of The Prior Art
In gas turbines, it is desirable to seal the space between the tips of rotating turbine blades and the surrounding casing by annular sealing means having a structurally strong outer annular base portion secured to the turbine casing or other parts thereof and an inner annular seal portion which, due to the small clearance required to minimize leakage, may actually be rubbed during operation by the rotating blade tips, which, when rubbed, will yield to the tips rather than subject them to significant damage. The foregoing statement also applies to seals around bearings, shroud seals and to the space between the inner bore of the stationary nozzle diaphragm assembly and the series of annular rib-like serrations conventionally provided on the adjacent portion of the rotating turbine core structure. Damage to the serrations on the turbine torque tubes or core is particularly to be avoided.
Typical annular tip seals, and, in some cases, core seals, are shown in the following U.S. Pats. viz: Bobo U.S. Pat. No. 2,963,307, which uses, for tip and core seal purposes, a series of spaced parallel "soe" strips (i.e. standing on edge strips) shaped with semi-hexagonal undulations secured together to form a conventional honeycomb; Morley et al. U.S. Pat. Nos. 3,082,010 and 3,092,393 which disclose tip seals composed of spaced parallel "soe" strips with means for spacing them; Desmond U.S. Pat. No. 3,694,884 which shows a tip seal composed of a singly corrugated "soe" strip mounted on a base ring; Moscowitz U.S. Pat. No. 3,867,071 which shows a tip seal composed of a series of corrugated "soe" strips mounted on a base ring, these strips comprising alternate "soe" strips having base portions only and interposed "soe" strips having both base and seal portions, the base portions of all strips cooperating to form a base honeycomb, while the seal portions of the interposed strips project beyond the base honeycomb in spaced parallel relationship; and Long U.S. Pat. No. 3,916,054 which shows, in FIG. 5, a series of corrugated "soe" strips mounted edgewise on an outer circular strip wherein the corrugations in alternate strips are slanted one way while those in the interposed strips are slanted in the opposite way, and, in FIGS. 6-12, various other corrugated arrangements which are similar except that, in FIG. 6, the alternate strip corrugations are radial, in FIG. 7, the alternate strip corrugations slant one way at one angle while the interposed strip corrugations slant the same way at a different angle, in FIG. 8, the alternate strip corrugations slant one way while each one in the interposed strips is "elbow" slanted, i.e. slanted 1st one way and then the other, in FIG. 9, the alternate strip corrugations curve radially one way while those in the interposed strips curve radially the opposite way, in FIG. 10, all strips have elbow corrugations containing slanted base and radial seal sections with the slanted base sections in the alternate strips going one way and, in the interposed strips, the other way, in FIG. 11, all strips have radial corrugations terminating at the base and seal ends in slanted portions, the slant of the alternate strips being the reverse of the slant of the interposed strips, and, in FIG. 12, the alternate strips have the elbow slant of FIG. 8 while the interposed strips have straight radial corrugations of FIGS. 6 and 12.